Mobile phones, and other devices having only a limited set of input keys, have become increasingly popular. While the numeric keys of a mobile phone are adequate for entering phone numbers and other number sequences, they are difficult to use for entering text. A standard keyboard has keys for both letters and numbers, whereas the numeric keys of a mobile phone have no intuitive way by which to enter text. Text may need to be entered on such devices, for example, to associate a name with a phone number in an address book. Since mobile phones and other such devices are becoming more popular for accessing the Internet, such as to browse web sites and send and receive email, this limitation will likely become increasingly acute in the future.
Currently, there are two common ways to achieve text input using numeric keys, a multiple-tap approach, and a single-tap approach. With the multiple-tap approach, a user presses a numeric key a number of times to enter the desired letter, where most of the numeric keys are mapped to three or four letters of the alphabet. For example, the two key is usually mapped to the letters A, B, and C. If the user presses the two key once, the letter A is entered. If the user presses the two key twice, the letter B is entered, and if the user presses the two key three times, the letter C is entered. Pauses between entry of successive letters of a word are often necessary so that the device knows when to advance the cursor to the next letter-entry position. For example, to enter the word “cab,” the user presses the two key three times to enter the letter C, pauses, presses the two key once to enter the letter A, pauses again, and presses the two key twice to enter the letter B. To enter numbers, symbols, or switch between upper- and lower-case letters, typically other keys that are present on numeric keypads, such as the pound (“#”) and asterisk (“*”) keys, among other keys, are mapped for these purposes.
While the multiple-tap approach is usable in that users can enter any word using only the numeric keys, it is disadvantageous for quick and intuitive text entry. A word such as “cab” that only requires three key presses on a standard keyboard, one for each letter, requires six key presses on numeric keys using the multiple-tap approach. As compared to using a standard keyboard, using numeric keys with the multiple-tap approach to achieve text entry means that the user presses many keys even for short messages. Furthermore, errors can be frequent. For example, if the user intends to enter the letter B, but pauses too long between the first and the second presses of the two key, two letters A will be entered instead. The device in this case interprets the pause as the user having finished with the current letter entry, an A, and proceeds to the next letter-entry position, where it also enters an A.
Another approach to text entry using numeric keys is the single-tap approach, which is also known as the Tegic approach, for the company that popularized it. Under the single-tap approach, the user presses the numeric key associated with the desired letter once, even though the numeric key may be mapped to three or four different letters. When the user is finished entering a number sequence for a word, the device attempts to discern the word that the user intended to enter, based on the number sequence. Each number sequence is mapped to a common word that corresponds to the sequence. For example, the number sequence 43556 can potentially correspond to any five-letter word having a first letter G, H, or I, since the four key is usually mapped to these letters. Similarly, the sequence potentially corresponds to any five-letter word having a second letter D, E, or F, a third and fourth letter selected from the letters J, K, and L, and a fifth letter M, N, or O, since the three, five, and six keys are usually mapped to these respective letters. However, because the most common five-letter word corresponding to the number sequence 43556 is the word “hello,” the single-tap approach always enters this word when the user presses the four, three, five, five, and six keys in succession to input this number sequence.
The single-tap approach has advantages over the multiple-tap approach, but presents new disadvantages. Advantageously, the single-tap approach ensures that the user only has to press the same number of keys as the number of letters in a desired word. For example, the multiple-tap approach requires the user to press the two key six times to enter the word “cab.” Conversely, the single-tap approach potentially only requires the user to press the two key three times to enter this word, assuming that the number sequence 222 is mapped to the word “cab.” Therefore, the single-tap approach is more key-efficient than the multiple-tap approach for text entry using numeric keys. It is as key-efficient as using a standard keyboard that has a single key for each letter.
The single-tap approach is disadvantageous in that the word mapped to a given number sequence may not be the word the user intended to enter by inputting the sequence. For example, the numeric key sequence 7333 corresponds to both the words “seed” and “reed.” Because only one word is mapped to each numeric key sequence, the word “seed” may be entered when the user keys in the numeric key sequence 7333, whereas the user may have intended to enter the word “reed.” The single-tap approach is primarily useful where there is only one unique word for a given numeric key sequence, or, if there are a number of words for a given sequence, when the user wishes to input the most common word associated with the sequence. For entry of uncommon words corresponding to number sequences to which words that are more common also correspond, the approach is less useful. The single-tap approach is also not useful for the entry of all but the most common proper names, and scientific, legal, medical, and other specialized terms, all of which will not usually be mapped to number sequences. Where the word mapped by the single-tap approach is not the intended word, text entry may revert back to the multiple-tap approach, or to an error-correction mode. Ultimate text entry of the intended word may then require more keystrokes than if the user had started with the multiple-tap approach.
The problem of a given number sequence mapping to multiple words is referred to as the ambiguity limitation of the single-tap approach. Some prior art approaches exist to overcome this limitation by attempting to disambiguate the intended word when the user enters a number sequence that corresponds to more than one word. One disambiguation approach is to show the user a number of different words that correspond to the entered number sequence, in order of decreasing frequency of use—that is, in decreasing order of how common the different words are. The user then selects a word from the list. This approach is described in detail in U.S. Pat. No. 5,953,541, issued on Sep. 14, 1999. The primary disadvantage to this disambiguation approach is that after the user has entered the number sequence, he or she is forced to expend additional effort reviewing the presented list of words, and selecting the desired word from the list. While this may be better than forcing the user back into a multiple-tap approach to reenter the intended word with additional keystrokes, it still can considerably delay text entry using numeric keys.
An improvement to this disambiguation approach is described in detail in U.S. Pat. No. 6,011,554, issued on Jan. 4, 2000, and which is a continuation-in-part of the patent application that issued as U.S. Pat. No. 5,818,437 on Oct. 6, 1998. Under the improved disambiguation approach, the word corresponding to the entered number sequence that has the highest frequency of use is automatically selected by default when the user begins to enter a new number sequence using the numeric keys. This is advantageous because, if the user's intended words are those having the highest frequency of use for the entered number sequences, the user does not have to select them from presented lists. However, at best occasionally, and at worst frequently, the user still has to select the desired word from a list, when the desired word is not the word with the highest frequency of use for the entered number sequence. This means that text entry delays are still inevitable even with this improved disambiguation approach.
Perhaps the primary disadvantage to either the original disambiguation approach, or the improved disambiguation approach, is that the order of words presented in the list intrinsically depends on only the current number sequence entered by the user. The described disambiguation approaches only consider the frequency of use of the words that correspond to the current number sequence in ordering the list of words from which the user can select a desired word. For a given number sequence entered, the list of words presented to the user is always the same. Therefore, using one of the previously described examples, when the user enters the number sequence 7333, if the word “seed,” which corresponds to this number sequence, has a higher frequency of use than the word “reed,” which also corresponds to the sequence, the former word is always displayed in the list ahead of the latter word. The list of words does not take into account that in some situations the word “reed” is a better choice than the word “seed.” As an example, if the user is entering the sentence “The first reed is shorter than the second reed,” the device will present the user with the word “seed” for both the first and the second time the user enters in the sequence 7333 for the intended word “reed.” The device does not discern that if the user has most recently selected the word “reed” for the sequence 7333, the user more likely wishes to enter this word, and not “seed,” when entering the sequence again.
The primary improvement that the described disambiguation approaches have over the single-tap approach is that they provide the user with a list of alternative words from which a less common word can be selected. The most common word, which is always selected by the single-tap approach, is still the word at the top of the list in the original disambiguation approach, and is the word that is selected by default in the improved disambiguation approach. The word selected by the device as the most likely intended word under all these approaches is still based on a commonality measure, or frequency of use measure, of the words corresponding to and considering only the entered number sequence. While these prior art approaches may successfully guess the intended word most of the time, they are still unsatisfactory. The user is still forced to at least occasionally select other words corresponding to entered number sequences, and not accept the proposed, most common words corresponding to the sequences. Furthermore, where the user is entering many proper nouns, or specialized, uncommon terms, the user is more likely to have to select other words corresponding to the entered sequences, and not accept the proposed, most common words corresponding to them, more often than not. For these reasons, as well as other reasons, there is a need for the present invention.